Stock Option Plan - Additional information (Detail) (USD $)	1 Months Ended	12 Months Ended					124 Months Ended	12 Months Ended				1 Months Ended												12 Months Ended		1 Months Ended								12 Months Ended		1 Months Ended										12 Months Ended
	Aug. 31, 2007	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2007	Dec. 31, 2013	Dec. 31, 2012 Employees	Dec. 31, 2012 Director	Dec. 31, 2012 Director Maximum	Dec. 31, 2012 Director Minimum	Dec. 31, 2013 Restricted Stock	May 31, 2013 Restricted Stock	Mar. 31, 2013 Restricted Stock	Jan. 31, 2013 Restricted Stock	Dec. 31, 2012 Restricted Stock	Jul. 31, 2012 Restricted Stock	Dec. 31, 2011 Restricted Stock	Jan. 31, 2011 Restricted Stock	Dec. 31, 2010 Restricted Stock	Sep. 30, 2010 Restricted Stock	Jan. 31, 2010 Restricted Stock	Dec. 31, 2009 Restricted Stock	Dec. 31, 2012 Restricted Stock	Dec. 31, 2011 Restricted Stock	May 31, 2012 Restricted Stock Employees	Feb. 29, 2012 Restricted Stock Employees	Jan. 31, 2012 Restricted Stock Employees	Dec. 31, 2011 Restricted Stock Employees	Jul. 31, 2011 Restricted Stock Employees	Dec. 31, 2009 Restricted Stock Employees	Sep. 30, 2009 Restricted Stock Employees	Dec. 31, 2008 Restricted Stock Employees	Jan. 31, 2008 Restricted Stock Employees	Dec. 31, 2007 Restricted Stock Employees	Dec. 31, 2013 Restricted Stock Non Employee Directors	Dec. 31, 2012 Restricted Stock Non Employee Directors	Feb. 29, 2012 Restricted Stock Non Employee Directors	Dec. 31, 2011 Restricted Stock Non Employee Directors	Jan. 31, 2011 Restricted Stock Non Employee Directors	Apr. 30, 2010 Restricted Stock Non Employee Directors	Mar. 31, 2010 Restricted Stock Non Employee Directors	Dec. 31, 2009 Restricted Stock Non Employee Directors	Sep. 30, 2009 Restricted Stock Board of Directors	Dec. 31, 2008 Restricted Stock Board of Directors	Dec. 31, 2013 Unvested Restricted Common Stock	Dec. 31, 2013 the "2003" plan	Jun. 23, 2010 the "2003" plan	Jun. 04, 2009 the "2003" plan	Apr. 25, 2007 the "2003" plan	Apr. 26, 2006 the "2003" plan	Dec. 21, 2004 the "2003" plan	May 31, 2012 the "2012 Plan"	Dec. 31, 2013 the "2012 Plan" Employees Maximum	Dec. 31, 2013 the "2012 Plan" Director Maximum	Dec. 31, 2013 the "2012 Plan" Consultants Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance		45,823					45,823																																								9,002,436	3,000,000	2,000,000	2,000,000	750,000	1,252,436	4,000,000
Outstanding options issued		6,747,303	7,147,303	5,138,486	4,566,935		6,747,303																																															5,834,408	912,645	250
Vesting period								3 years		3 years	2 years															3 years	3 years	3 years	3 years	3 years	3 years	1 year		3 years		1 year	3 years		3 years	3 years	1 year	1 year	2 years	1 year
Contractual terms								10 years	10 years
Compensation expenses		$ 3,507,000	$ 4,880,000	$ 2,759,000	$ 27,000	$ 120,000						$ 1,200,000				$ 1,700,000		$ 635,000						$ 1,700,000	$ 635,000
Options vested in period					6,904	25,111
Options exercised	25,111	570,168	8,300	479,666
Proceeds from stock options exercised	50,000	956,000	30,000	980,000			2,329,000
Total intrinsic value of options	104,000	1,400,000	11,000	2,500,000
Unrecognized compensation costs		$ 8,500,000					$ 8,500,000																																							$ 1,300,000
Expected recognition period		1 year 10 months 2 days																																												1 year 5 months 12 days
Share-based payment award granted		75,272	258,032	848,406																						25,000	43,802	101,500	720,675	50,000	347,500	828,000	396,500	100,000	70,000	75,272	87,730	43,802	52,731	25,000	25,000	90,000	45,000	180,000	90,000
Repurchase of shares of restricted common stock												56,683	2,623	5,400	52,018	107,413	15,740	44,369	15,190	51,116	349,710	15,283	103,823
Repurchase of shares of restricted common stock, price per share												$ 4.37	$ 1.65	$ 4.50	$ 4.28	$ 4.19	$ 6.06	$ 4.41	$ 5.14	$ 4.66	$ 3.95	$ 3.10	$ 3.66